Flow and aspiration of artificial feeds through nasogastric tubes

The physical characteristics of 12 nasogastric tubes (Clinifeed, Portex prima, Vygon 6 and 9, Dobbhoff, Nutriflex and 6 Ryles tubes) and 13 feeds (4 Clinifeed Preparations, Nutranel, Nutrauxil, Express, Triosorbon, Fortison, Enteral 400, Elemental 028, Complan and Complan + Caloreen have been assessed under laboratory conditions. The accuracy of the stated internal diameter of the tubes tested varied from 88-119%. The rate of flow was inversely related to the length of the feeding tube and was greatly affected by diameter (an increase from 1 to 2 mm increased flow 10-fold); and was virtually unaffected by the side holes at the end of the tube. Giving sets provide only a small resistance to flow. The viscosities of liquid feeds did not correlate with their osmolarities. The values ranged from 1.9-28 centipois (cps) at 24 degrees C and universally decreased to 1.4-19 cps at 37 degrees C. All enteral feeds except Clinifeed 500, flow satisfactorily through fine bore tubes under a low head of pressure. Undiluted Clinifeed 500 (a high protein feed) requires pumping. Feeds containing casein (e.g. Complan, Nutrauxil, Fortison, Triosorbon) curdle in the presence of acid which hinders aspiration through even widebore tubes. Foods containing whey protein (Express, Enteral 400) or no protein (Elemental 028) do not coagulate with change of pH. Batch to batch variations in liquid feeds are usually small but with one preparation were sufficiently large to cause problems in delivery. The results of these studies provide further data on which to base the choice of liquid feed and giving tubes in clinical practice.